Eastern Libyan forces have seriously damaged with air strikes a civilian airport in western Libya lacking any military use, the United Nations said on Sunday.

Last week, the eastern-based Libyan National Army (LNA) said it had twice bombed the airport of Zuwara, a town west of capital city of Tripoli, saying it had targeted hangars used by Turkish drones.

The attacks are part of a campaign currently in its fifth month to take Tripoli held by the country's internationally recognized government. The LNA is commanded by Khalifa Haftar.

The UN Libya mission (UNSMIL) said in a statement it had visited Zuwara airport and found no military infrastructure or assets.

"The Mission renews its condemnation of the attacks conducted by the LNA forces against Zuwara airport, which cause serious damage," it said, adding that the runway had been damaged.

The LNA also flew several sorties late on Saturday for air strikes on an air base in the western city of Misrata, whose forces are helping to defend Tripoli, local residents said.

"Three massive explosions could be heard," said one resident.

The LNA could not be immediately reached for comment.

The LNA has resorted to increased air strikes against Tripoli airport and other targets since its ground campaign has failed to make it beyond southern suburbs of the Libyan capital.

Turkey has supplied the Tripoli forces with drones and trucks to match military support by Egypt and the United Arab Emirates for the LNA, according to diplomats.

The conflict is part of chaos gripping Libya since the toppling of the country's former leader Muammar Gaddafi in 2011.